The effect of hibernation status and cold-acclimation on hepatocyte gluconeogenesis in the golden-mantled ground squirrel (Spermophilus lateralis)

Rates of gluconeogenesis were measured in hepatocytes isolated from torpid, aroused, summer-sampled non-cold-acclimated, and summer-sampled cold-accli mated Spermophilus lateralis. At 7 degrees C, no not glucose synthesis is m easurable. At 37 degrees C, 10 mM alanine supports low rates of gluconeogen esis that do not differ among groups. With 10 mM lactate/1 mM pyruvate, rat es of gluconeogenesis are 60% higher in the torpid group than iri the summe r non-cold-acclimated group. With 10 mM glycerol, rates of gluconeogenesis are 2-fold higher in the torpid, aroused, and summer cold-acclimated groups than in the summer non-cold-acclimated group. The higher rates of gluconeo genesis with lactate/pyruvate and glycerol are probably more related to col d-acclimation than to hibernation/seasonal status per se, as no differences were noted among the cold-exposed groups. The observed differences in rate s of gluconeogenesis cannot be readily explained by differences in apparent oxidative efficiencies of gluconeogenesis or activities of key gluconeogen ic enzymes, but may be related to a general upregulation of hepatocyte meta bolism accompanying cold-acclimation. This is reflected in the higher rates of hepatocyte oxygen consumption in the cold-exposed groups. Increased bio synthetic capacities during the winter season may not be a specific adaptat ion to hibernation, but may still contribute to energy savings over the hib ernation season by helping to minimize euthermic arousal intervals.